1. Field of the Invention
The invention relates to the art of oil well drilling and to the equipment used therefor, particularly, to automated apparatus for handling elongated well elements such as pipes especially used in well bore repairs on offshore drilling platforms.
2. Description of the Prior Art
During oil well operation there is a frequent need of carrying out preventive maintenance operations as well as special repairs which require manipulating of damaged equipment into and out of a well, the equipment including drill pipes and rods that got out of order in a drill string.
With the aim of performing these operations a mobile apparatus is erected over the well bore to generally include hoisting means, gripping and rotating means adapted to screw and unscrew the joints on a string of drill pipes or rods. Since well servicing is performed on an operating well, efficiency is very important. Well servicing time also includes the time for raising and lowering drill strings and in all instances it is desirable to reduce this time to a minimum. The quest for time reduction in performing the above operations has led to improvemets in timed coincidence of the operations, on the one hand, and also in automation of these operations. To the accomplishment of the first of the above trends there have been proposed apparatus in which not only the lowering and raising operations coincide with loading and unloading operations, but idle time and no-load lowering and raising of the equipment for suspending the string of pipes or rods have been eliminated while in some drilling installations the screwing and unscrewing of pipes and similar elongated well elements (drill-pipe stand, rods) are carried out simultaneously with continuous lowering or raising of the string composed of such elongated well elements (see, for example, U.S. Pat. Nos. 3,194,313; 3,306,101; 3,376,938; 3,404,741; 3,861,756; Soviet Inventor's Certificate No. 629,314).
However, attempts to make such apparatus economically feasible failed because the aforesaid solution inevitably involves complications in structure caused by the necessity to manipulate in parallel by at least two elongated well elements to be screwed or unscrewed to form a string. In this case the control system of the apparatus becomes substantially complicated to therefore decrease reliability of the system.
That is why alongside with the above mentioned apparatus, which may be referred to as continuous action apparatus, there are designed and find an extensive application apparatus offering lesser coincidence in the operations, such apparatus being further referred to as discontinuous action apparatus (see, for example, U.S. Pat. Nos. 3,239,016; 3,266,582; 4,042,123). In such an apparatus emphasis is mainly placed upon economy, safety, and reliability in operation, decrease in overall dimensions, especially in clear height, and specific amount of metal per structure. These qualities are especially important for operating marine wells. Thus, in designing both the continuous action apparatus and the discontinuous action apparatus there is a tendency to automate the operations as much as possible with the end of increasing operating efficiency and safety.
One of the major problems encountered while designing a fully automated apparatus is associated with different lengths of pipes or similar elements forming part of a well string. Commercially known drill pipes and rods have a length tolerance within .+-.50 mm. Therefore, while manipulating a single pipe or rod the position of its end may vary within 100 mm. When a string consisting of several well elements is raised in increments with each increment being equal to a rated length of a single well element, total displacement of the string end may amount to several meters, which is why the apparatus will not operate without position adjustments of its mechanisms.
The automated system disclosed in Soviet Inventor's Certificate No. 629,314; Int.Cl..sup.2 E. 21B 19/16, granted in 1974, and offering a continuous operation, is a solution to the problem of rendering the operating cycle automatic with due regard to different lengths of the well elements.
That automated system comprises derrick-mounted and vertically movable upper and lower means for suspending a string of well elements, the means being carriages with elevators, a manipulator for delivering a well element (a stand of pipe) from a storage means (a stand receiver) to the well bore, the manipulator comprising two rotating levers for delivering a stand of pipe, and an automatic tong having a high-torque device (a tightener wrench) arranged on the lower carriage and a low-torque device (the tong proper) mounted on a further vertically movable carriage arranged above the carriage of the upper means for suspending the well string. Each of the carriages is provided with an individual drive for vertically moving a respective carriage. The elevator, the manipulator, and the high-torque device each comprise grippers kinematically connected to drives for opening and closing the same grippers. The grippers of the low-torque device are kinematically connected to a drive for horizontally moving the same grippers. Both the elevators and the grippers of the low-torque device are vertically movable relative to the carriages on which they are mounted.
The control system of that automated system comprises carriage position sensors, sensors for sensing the position of the elevators relative to the carriages, sensors for sensing the position of the grippers on the well axis, sensors for sensing the position of the grippers, sensors for sensing the position of a well element in the string (these are sensors for sensing the presence of a stand lock as disclosed in the specification of the Inventor's Certificate). All the above mentioned sensors are connected through a control device with the respective drives of the above disclosed mechanisms of the automated system.
The control system provides for continuous lowering or raising of the well string by the movable elevators which in turn take up the weight of the string, while the screw is tightened or loosened by the high-torque device and screwed and unscrewed by the low-torque device at the same time as the elevators move vertically. A further stand of pipe is simultaneously delivered from the stand receiver to the grippers and in the opposite direction. The displacement of the upper end of the string and the lower end of the stand of pipe to be connected to or disconnected from the upper end of the string is compensated by the movement of the elevators relative to respective carriages and by the vertical displacement of the grippers of the low-torque device relative to its carriage. One of the sensors serves to sense the presence of a stand lock in the grippers of the device. A similar sensor is provided on the upper elevator and controls withdrawal of the grippers of the low-torque device, which hold an unscrewed stand, from the well axis as the string is raised or produces a control signal for halting the same grippers, which hold a stand to be screwed, on the well axis as the string is lowered.
Thus, the just described automated system offers improved efficiency in lowering and raising drill string elements due to both an extensive use of automation and to coincidence in time of the most operations performed by the system. As can be seen, however, even from this simplified description, this automated system has a complicated structure due to a great number of movable units, such as carriages, elevators, a tong, a respective number of drives, and a great number of control instruments. As a result, the system is cumbersome, its specific amount of metal is great and so is the weight, on the one hand, and on the other hand, it has inevitably inadequate reliability in operation. Also, these same features in combination with a relatively high derrick, which in this construction should measure more than two lengths of a well element, render this system inappropriate for use on offshore drilling platforms due to a limited floor area on such platforms and a limited supply of repair means, as well as due to the requirement of increased stability of the platform intended to support this system.
The above problem of compensating unequal lengths of well elements was repeatedly a major obstacle in achieving complete automation in the discontinuous action systems, which are structurally simpler than the one just described. In search of the ways to a solution of this problem, AUTOMATIC DRILLING MACHINES, INC. decided to order a special-gage drill string consisting of pipes equal in length, or more precisely, of pipes made to close tolerances for length.
An automated drilling apparatus designed by the above company, which can be simultaneously used for performing both lowering and raising operations in repairs, comprises an upper means and a lower means both for suspending a drill string, an automatic tong for screwing and unscrewing the well elements, and a manipulator for delivering a well element to an operating position along the well bore axis. The upper means is a drill bit mounted on the derrick for vertical movement and kinematically connected to a respective drive constructed as a hydraulic hoisting system. The drill bit operates as a low-torque device of the automatic tong, the other part of which is represented by mechanisms arranged in a chuck of a suitable design. Three sets of grippers are arranged in the upper portion of the chuck together with a drive for closing and opening the same grippers and with a rotary drive operate as a high-torque device, while the remaining grippers together with the drive for closing and opening the grippers operate as a locking device. The lower means for suspending the drill string is represented by a spider having wedge-shaped grippers (a pipe holder) and assembled under the chuck. The manipulator is a shift lever rotatable in a vertical plane, provided with power grippers and with a drive for effecting movement of the lever both ways in an operating position (horizontal) and in an operating position (vertical).
The apparatus also comprises an automated pipe racking stand for storing drill pipes in a horizontal position. The pipe racking stand is provided with storage racks arranged at both sides from the manipulator and constructed as magazines having rows of vertical posts to accomodate the pipes therebetween so that their axes are parallel to the axis of a pipe gripped by the grippers of the manipulator when the latter is in a horizontal position.
Cranes serves as a transfer device to transfer pipes from the pipe storage racks to the manipulator. Each crane comprises a movable member which can move in both a vertical and horizontal planes. The movable member is a transverse-piece installed in horizontally extending guides for movement perpendicularly to the pipe axis (a transverse direction) and supporting a beam having grippers, the beam in turn being suspended on a leverage for movement up and down. For performing all kinds of movements there are drives provided in the apparatus. The pipe storage racks are arranged on individual trailers. The drives of the apparatus are hydraulically operated. The control system comprises a programmed logical control unit having an input terminal connected to the sensors and to a control console, and an output terminal connected to a system of electrically controlled actuators which set in motion the drives of the apparatus (see J. A. Castrop, U. B. Colwin "Avtomatizirovannaya burovaya ustanovka s gidravlicheskoi gruzopodyomnoi sistemoi", U.S. monthly "Inzhener-neftyanik"/Russian translation/, No. 3, 1967, p. 29-36).
The apparatus is a small-bulk arrangement both in height (under 12 m) and in floor area, and it is simple in construction and extensively automated to provide practically automatic operation. However, while manipulating a string of drill pipes, positioning of the string in the chuck, requiring a strict matching of jaws with the lock of the string, has to be adjusted from the control console. In order to determine the misalignment of the end of the string in the chuck there is a TV camera provided in the apparatus with a TV screen on the control console.
The special-gage drill string consisting of pipes equal in length renders the apparatus expensive and inconvenient in repairs. On the other hand, utilization of conventional pipes would impede efficiency because some operations in lowering and raising the pipes would have been carried out under normal control. This in turn would risk reliability and safety to thereby make the control of the apparatus dependent on the skill, experience, and psychological characteristics of the operator.
A disadvantage of the apparatus also resides in the fact that some conventional pieces of equipment (e.g. an automatic tong) used therein are of special design, which accounts for a high cost of production.
Also, the fact of utilizing cranes as a means for transferring pipes from the storage racks to the manipulator and back accounts for awkwardness and high specific amount of metal per automated pipe racking stand, while the storage rack per se, though simple in construction, impedes control of the pipe racking stand, which control is to provide variations in positioning of the grippers of the transfer device in a two-dimensional coordinate system.
Moreover, the automated pipe racking stand is inconvenient for transportation since an additional vehicle is required.
Furthermore, the storage rack design offers accomodation for pipes of one and the same diameter. Pipes of a different diameter may be accomodated after changing the magazines.